1. Field of the Invention
The present invention relates to unmanned helicopters and more specifically to an unmanned helicopter including a drive shaft.
2. Description of the Related Art
An example of a conventional unmanned helicopter is disclosed in JP-Y H6-6876. JP-Y H6-6876 discloses an unmanned helicopter including a transmission shaft (drive shaft) that transmits a rotation torque to a tail rotor; a tail boom that supports the transmission shaft; and a cosmetic cover that covers an outer circumferential surface of the tail boom. In this arrangement, an elastic member is located between the outer circumferential surface of the tail boom and the cosmetic cover which opposes the tail boom.
An unmanned helicopter such as the one described above requires exact control on the number of rotations of the tail rotor to control the helicopter's attitude. In order to achieve this, a desired rotation torque must be transmitted to the tail rotor via the tail boom.
However, in the unmanned helicopter disclosed in JP-Y H6-6876, there can be a problem that if a high-frequency, high-amplitude variation in the number of rotations is caused in the transmission shaft by a hunting phenomenon from an engine rotational variation or the like when the tail rotor is rotated, a large rotation torque will result in the transmission shaft due to the variation in the number of rotations.